Method of determining a formation parameter

Abstract

A method of measuring a formation parameter in the process of drilling a well penetrating the rock formation is disclosed. A section of the well is provided with a drill string comprising a drilling bit at its distal end; a first fluid is circulated through the drilling bit and invades the rock formation; a formation evaluation tool mounted onto the drill string is used to measure the formation parameter; the formation parameter is used to select the time at which a second fluid is circulated through the drilling bit; such that the second fluid alters the response of the rock formation to the formation evaluation tool; the second fluid is circulated through the drilling bit to start invading the formation; and the formation evaluation tool is used to repeat the measure of the formation parameter while circulating the second fluid.

What is claimed is: 
     
       1. A method of measuring a formation parameter of a rock formation in the process of drilling a well penetrating the rock formation, comprising:
 providing a section of the well with a drill string comprising a drilling bit at a distal end of the drill string; 
 circulating a first fluid through the drilling bit, said first fluid invading the rock formation surrounding the well; 
 using a formation evaluation tool mounted onto the drill string to measure the formation parameter; 
 selecting a time at which a second fluid is started to circulate through the drilling bit, such that the second fluid alters a response of the rock formation to the formation evaluation tool; 
 circulating the second fluid through the drilling bit to start invading the formation surrounding the well; and 
 using the formation evaluation tool to re-measure said formation parameter while circulating said second fluid. 
 
     
     
       2. A method in accordance with  claim 1 , further comprising removing layers from a wall of a section prior to circulating the second fluid. 
     
     
       3. A method in accordance with  claim 1 , wherein the rock formation includes hydrocarbon bearing rock. 
     
     
       4. A method in accordance with  claim 1 , wherein the formation evaluation tool is selected from a group comprising nuclear magnetic resonance tools, neutron scattering or capturing tools, sonic tools and resistivity tools. 
     
     
       5. A method in accordance with  claim 1 , wherein the first fluid is a drilling fluid. 
     
     
       6. A method in accordance with  claim 1 , wherein the second fluid comprises a component miscible with either hydrocarbon or water. 
     
     
       7. A method in accordance with  claim 1 , wherein the second fluid comprises a paramagnetic material altering the response of the rock formation to the formation evaluation tool. 
     
     
       8. A method in accordance with  claim 7 , wherein the paramagnetic material comprises manganese, chromium. 
     
     
       9. A method in accordance with  claim 1 , wherein the second fluid comprises chlorine. 
     
     
       10. A method in accordance with  claim 1 , further comprising using the formation evaluation tool to perform a time series measurement of the parameter while circulating the second fluid.